Leukotriene B4 (LTB4) is a distinct isomer of 5,12-dihydroxyeicosate- traenoic acid, which is generated by the 5-lipoxygenation of arachidonic acid in immunologically-activated mast cells, leukocytes, and some other types of cells. LTB4 is a potent mediator of diverse functions of polymorphonuclear (PMN) leukocytes and lymphocytes, as well as of endothelial, smooth muscle, and epithelial cells. The time-course of appearance and concentration of LTB4 in some human inflammatory lesions have suggested a pathogenetic role in cutaneous allergies, asthma, gout, spondyloarthritides, and rheumatoid arthritis. Responsive cells recognize LTB4 stereospecifically through one or more sets of plasma membrane receptors, which associate with Gi proteins. The results of the research proposed will increase our understanding of the genetic determinants, protein structure, and cellular properties of human leukocyte receptors for LTB4. The recent cloning and sequencing of a cDNA encoding the LTB4 receptor protein of human PMN leukocytes now will permit studies of the genetic control of receptor production and functions. The genomic organization and 5'-regulatory regions of the LTB4 receptor gene will be delineated and the pathways for processing newly-generated LTB4 receptor protein will be defined in cell-free model systems. The receptor protein structures required for cellular expression, as assessed by immunological and functional criteria, and for LTB4-binding specificity will be evaluated with mammalian cell transfectants bearing wild-type and various mutant receptors, in parallel with native leukocyte receptors. Selected biochemical and cellular characteristics of signal transduction by LTB4 receptors will be elucidated, including association with guanine nucleotide binding Gi proteins. effects on [Ca++]i and polyphosphoinositide- metabolism, regulation of membrane potential and ion transport, and LTB4- induced desensitization of LTB4 receptors. The distribution of LTB4 receptors on immune cells and in tissues responsive to LTB4 will be determined with both oligonucleotide probes and anti-receptor antibodies, in several models of cutaneous and pulmonary hypersensitivity. The resultant knowledge of LTB4 receptors on leukocytes and other cells will elucidate some mechanisms of immune induction of inflammation and other elements of hypersensitivity and may provide useful new tools for diagnosis and treatment of immunodeficiencies, allergic diseases, and autoimmunity.